Bit-Twist is a libpcap-based packet generator and packet capture file modifier and replayer. It complements tcpdump, a packet capturing tool also built upon the packet capturing engine libpcap. Bit-Twist allows you to regenerate packets from one or more pcap files. It also comes with a comprehensive pcap file editor to allow advance manipulation of packet information, e.g. fields in Ethernet, ARP, IP, ICMP, TCP, and UDP headers, prior to regenerating the packets onto the network.